I have the latest DeDRM plugins from Alf's site. Whenever I drop an EPUB file into Calibre, even an EPUB with no DRM, I get an error message stating "Plugin not configured! Decryption unsuccessful." The error message goes on to say that this may be the first time I have used the plugin, and that I should go into Preferences to configure it. As I said, this happens with every EPUB import, even when the file does not have any DRM. It does not happen with MOBI files.

This started when I recently updated the plugins to the latest version.